This invention relates generally to electrical circuit interrupters and more particularly concerns current limiting breakers using a plurality of micromechanical switches. As used herein, the term "micromechanical" refers to miniscule devices which are fabricated using the technology of micromachining; this involves no assembly operations, but only the selective deposition and removal of materials on a substrate.
Circuit interrupters are designed to protect electrical equipment from damage caused by short circuit faults. Most conventional circuit interrupters are primarily bulky mechanical switches. These devices are capable of sensing a short-circuit current and interrupting the same by opening the switch via a heavy trip mechanism. Typical alternating current circuit breakers require the creation of a large mechanical gap between the contacts of the switch and can only interrupt an alternating current at a zero-crossing. More recently developed current limiting breakers provide the capability of substantially immediately interrupting alternating currents of high magnitude without waiting for a current zero-crossing. However, conventional current limiting breakers are typically complex in construction and thus somewhat expensive to fabricate.
The switch contacts of conventional circuit interrupters require a large contact force be maintained to prevent "popping, " i.e., the unwanted separation of the switch contacts which results from a current-induced repulsive popping force. The contact force is typically provided by adding weight to the contacts and/or adding structure, such as one or more springs, to exert force on the contacts. These measures increase the total weight and cost of the device. A second consideration is that once a short circuit fault is detected, the contacts of the circuit interrupter must be driven apart very rapidly to avoid arcing between them. But since conventional devices typically use heavy mechanical contacts, they either take a relatively long time to open the contacts or consume a large amount of energy to generate a force sufficient to separate the contacts quickly. Thus, conventional circuit interrupters tend to be relatively heavy devices which require high amounts of energy to operate.
Accordingly, there is a need for an electric circuit interrupter in which the overall popping force is reduced, thereby reducing the required contact force. An additional need exists for a circuit interrupter having means for rapidly separating the switch contacts without large energy requirements. Meeting these needs will provide a circuit interrupter which is lightweight and inexpensive to manufacture and requires less energy to operate than conventional devices.